High power terahertz production from relativistic electron beams

George R. Neil ^* and Gwyn P. Williams (retired)
Thomas Jefferson National Accelerator Facility
^* Email: neil@jlab.org

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Abstract: Relativistic electron beams are highly suitable as generators of high power terahertz radiation. The intensity of the radiation is greatly enhanced by the y⁴ scaling of synchrotron emission. In addition it is possible to take advantage of collective effects. For wavelengths longer than an electron bunch the electric fields coherently add and the power scales in quadrature. Given that typical electron bunches in accelerator-driven relativistic electron beams contain on the order of 10⁹ electrons, this enhancement factor can be significant. For single bunches of electrons undergoing transverse acceleration such as bending in a static magnetic field, the radiation is broadband and the enhancement extends in wavelength from the beampipe dimensions down to the electron pulse length [1].

Collective effects also can be enhanced in devices such as free electron lasers (FELs) where the electrons undergo microbunching at the optical (in this case terahertz) wavelength and the radiation becomes narrowband and fully coherent [2]. FELs have been around since 1977 providing not only a test bed for the physics of optics and electron/photon interactions but as a workhorse of scientific research. Recent extensions in average current by the application of energy recovery to the accelerator [2, 3] further enhance the power capability of these systems. The characteristics that have driven the development of these sources are the desire for high peak and average power, high micropulse energies, wavelength tunability, timing flexibility, and wavelength production unavailable from more conventional laser sources. Operation of FELs in the FIR to THz regime poses special challenges which have been and are being addressed at a number of facilities around the world. This talk will review the mechanisms of radiation production by relativistic electron beams both as broadband collective sources and coherent sources such as FELs. We will give status and examples of linacs and FELs operating in this regime and discuss future efforts. Applications for use of the radiation have evolved from simple imaging to complex pump probe tests of insulator/metal transitions and energy flow in organic molecules. We will also discuss the technologies for generating and controlling the IR/FIR/THz radiation and mention some of the unique applications of such sources.

Keywords: Terahertz, Free electron laser, Accelerator.

Received: 2015-6-5

Published: 2015-6-30

Cite this article:
George R. Neil and Gwyn P. Williams. High power terahertz production from relativistic electron beams[J]. International Journal of Terahertz Science and Technology, 2015, Vol.8, No.2: 41-54.  DOI:10.11906/TST.041-049.2015.06.05

URL: http://www.tstnetwork.org/10.11906/TST.041-049.2015.06.05